This invention relates to an improvement in a packaging machine, and more particularly to a packaging machine in which a belt-shaped packaging sheet fed continuously by feeding means is cut to a predetermined length by cutting means while being guided and conveyed in a direction intersecting the conveyance direction of articles to be packaged. Also, the packaging sheet is folded in two to package each article as the article is conveyed.
The packing sheet in this invention has a base material such as paper, cellophane, plastic or the like. It is wound in the form of a roll. In the packaging operation, the packaging sheet in the form of a roll is unwound and cut to a predetermined length, to package an article.
Conventional packaging machines have a belt-shaped packaging sheet fed continuously by feeding means and the sheet is cut to a predetermined length by cutting means while being guided and conveyed in a direction intersecting the conveyance direction of articles to be packaged. The packaging sheet is folded in two to package each article as the article is conveyed. This system has disadvantages in the following aspects. As shown in FIG. 1, when the open sides of the packaging sheet which has been folded in two as described above are sealed by heat-welding, gluing or the like, the open edges e and e' of the two portions of the packaging sheet B which overlap one on another to package the article A are shifted from each other as indicated by d. This shift will impair considerably the packaging effect and the appearance of the package.
This shift difference d is due to the packaging sheet feeding mechanism in the conventional packaging machine. More specifically, in the packaging sheet feeding mechanism in the conventional packaging machine, in general, a feeding roll adapted to feed the packaging sheet wound in the form of a roll, and a cutter drum with a cutter for cutting the fed packaging sheet in the widthwise direction are provided as one unit, and the diameter of the cutter drum is set so that its circumference is equal to the whole length of the packaging sheet required for one package. Therefore, if the timing at which the article to be packaged is conveyed to the surface of the packaging sheet is only slightly varied or the packaging sheet feeding speed fluctuates, the variation results in the shift at a distance d as described above.
In general, a thin packaging sheet is expanded or contracted under environmental conditions such as temperature and humidity or by tension, depending upon its composition. Therefore, the length set on the cutter drum or the like is unavoidably somewhat different from the length of the packaging sheet actually cut. Thus, it is necessary to provide a technique adapted to correct the above-described shift d for the device which feeds and cuts the packaging sheet having such elasticity. However, since the diameter of the cutter drum is preset in the packaging sheet feeding mechanism of the conventional packaging machine, different cutter drums or feeding rolls must be used for packaging articles different in size. That is, the cutter drum or the feeding roll must be exchanged for another one whenever the size of articles to be packaged is changed. This exchange is rather troublesome and decreases work efficiencies.